Access floors are raised above base floors typically fashioned of concrete, and provide access for cables, pipes, ducts and other utility or supply lines, equipment, and equipment hookups. Access floors are normally made of large, lightweight floor plates supported by a supporting substructure positioned on the base floor. Typical substructures incorporate pedestals and/or stringers. In most instances the pedestals of known substructures are braced to the base floor and/or to each other, which transfers lateral loads between the floor plates and stringers and the base floor. Lateral loads can originate above the access floor in some instances, such as from the rolling resistance of equipment moving thereacross. Seismic load is mainly a lateral load, which originates on the base floor and is transmitted to the access floor through the substructure supporting it above the base floor, and further to equipment resting on the access floor.
Existing raised access floors and their associated supporting substructures prove adequate, but it has been noticed that known raised access floors actually amplify base floor accelerations, which often results in damage to equipment and fixtures positioned thereon, such as server racks, main frame computers, electronics cabinets, semiconductor tools and manufacturing equipment, etc., which is obviously problematic, especially when such access floors are installed in geographical areas prone to seismic activity. Although there has long been a need in the art to provide a seismically-isolated raised access floor, none that is practical and economically feasible has yet been introduced in the art. Although some skilled artisans have attempted to isolate access floors by mounting the understructure over heavy-duty steel or aluminum or sheet metal framing of beams and columns and large seismic isolators, this structure not only does not satisfactorily provide the desired seismic isolation, but also encroaches into most of the usable access space and is complicated to build and install, expensive, and imposes large punching shear on the concrete floor, and thus proving to be unworkable and impracticable in the marketplace.